texts: .2015: When last did both New/Full moon in a fort-night cause an Eclipse?

texts:
Going through http://earthsky.org/…/dates-of-next-lunar-and-solar-eclipses I made the (what was for me - momentous) discovery that

March 20, 2015 - New moon - is a Solar Eclipse, and that the succeeding
April 04, 2015 - Full moon - heralds a Lunar Eclipse.

Is it common that both New/Full moon in a fort-night cause an eclipse?
When was the last time an Eclipse occurred back-to-back on a consecutive New Moon/Full Moon?


texts: Is "Giga-hertz Astrophysical Transient Emission" distinct in any way from "Fast Radio Burst"?

texts:
In this answer I have just read about The University of Texas Rio Grande Valley's The Spacecraft Tracking and Astronomical Research into Giga-hertz Astrophysical Transient Emission (STARGATE).

While Fast Radio Bursts (FRBs) seem to fit that description spot-on, I am wondering if the phrase was chosen to be in some way broader or more general than FRB to include other phenomenon, and if so, have there been any Giga-hertz Astrophysical Transient Emissions observations that are not also considered FRBs?

$\hspace{4cm}$

above: Logo of The University of Texas Rio Grande Valley STARGATE program.


texts: When can I see the Milky Way from the Earth?

texts:
Light pollution is restricting most people from ever seeing the Milky Way from the Earth.

Is there any place in India where I can see the Milky Way?

Is there a database or site with the list of all places where I can see it?

Also, how can we calculate that?


texts: Are occultation observations used/useful for orbit determination?

texts:
The IAU Minor Planet Center lists $(486958)\space 2014 \space MU_{69}$ "Ultima Thule" as having an uncertainty parameter of 2, based on the observation arc of 851 days, from its discovery in 2014, to the last observation submitted from Hubble in 2016.

Other sources indicate that there have been a number of ground-based observations of Ultima Thule occulting various background stars. Are these "observations" purposely not included/submitted as further sightings to increase the observation arc?


texts: Did the density wave theory for spiral arms take account of this phenomenon?

texts:
I came across this link. In it the author speculates that in the outer region of a galaxy, the spiral arms overtake the stars, and vice versa for the inner region. That means there must be a middle region where the speed of the arms and the stars are similar. Since the stars there are big, blue and short-lived, they must die quickly. But because no other stars or clouds are moving into this region because of the same speed, it will turn dark quite fast in cosmic terms.
The result is, every spiral galaxy should have a distinctive dark, round disk of 'nothingness' somewhere between the central core and the outer rim. Looks like it's not the case. How can we explain this discrepancy?


texts: Does the given radius of a planet/moon include its atmosphere?

texts:
In NASA fact sheets, such as this one for Venus, a radius of the planet is given.

Is that radius the radius of the surface of the planet, or of the envelope of atmosphere?

Put another way, if calculating the angular diameter of a planet/moon from a location, do I only have to look up this radius, or do I have to look up this radius along with the atmosphere height to determine the angular diameter?


texts: Rising & Setting time of a star on a specific date

texts: Given the local sidereal time (LST) of a star when it rises, how can I find out the time when it will rise (according to my watch) on a specific date?


texts: I need a stellar mass database that also has the distance of the star/system from the sun. Can anybody tell me the name of such of database and where I can find it. I need to do a project on this. Thank you for the answers.


texts: Which is a better way to increase magnification - by choosing an eyepiece of lesser focal length or by choosing a telescope with higher focal length?

texts:
Magnification of a telescope = (focal length of telescope / focal length of the eyepiece being used)
$$M=\frac{f_{objective}}{f_{eyepiece}}$$
If I want 75 X magnification and the following are the two ways being considered for obtaining that magnification, which one is better? What are the trade-offs and effects on the quality of observation? Where will I get a sharper image?
Method 1: Use telescope of 600mm focal length and an eyepiece of 8mm - giving magnification = 75 X
$$M = \frac{600\,mm}{8\,mm}=75$$
Method 2: Use telescope of 1200mm focal length and an eyepiece of 16mm - giving magnification = 75 X
$$M = \frac{1200\,mm}{16\,mm}=75$$
Assume that the telescope aperture is the same in both cases.
Any references are also welcome.


texts: Advice on first Telescope (refractor vs reflector), Barlow lens

texts: I am planning on buying my first telescope. I am getting an 80mm refractor and a 114mm reflector for the same price range. Which would be a better option? Further, would a Barlow lens solve the chromatic aberration issues with a f/5 refractor?


texts: Could a planet form without a molten state?

texts: Based on what I know, the Earth accreted out of the solar nebula, had a period when it was entirely molten, and then slowly cooled. Could a planet form without ever passing through a molten phase?


texts: How to find the distance between two galaxies from ra and dec and redshift

texts:
I have ra and dec and corresponding redshift of galaxies. I would like to calculate the distance between two galaxies.
I did like this to find the nearest neighbour galaxies.
Suppose I am trying to find the nearest neighbour of galaxy A(which has RA,DEC)  and the target galaxy has ra1,dec1,
so to find the distance between two galaxy, I did like this
dist_sqd= sqrt( (RA-ra1)**2 + (DEC-dec1)**2 )
#RA, DEC are in degree

Is this the correct way to find the distance.
As there is projection in 2D, Since, I already have redshift, Is there any best way to find the distance between two galaxies properly?


texts:
I am having trouble finding data on this. So far, I have found at least seven values:

1: 1.9885  e30 kg
2: 1.98855 e30 kg
3: 1.9891  e30 kg
4: 1.991   e30 kg
5: 1.989   e30 kg
6: 1.99    e30 kg
7: 2       e30 kg

The first value can be found from NASA GSFC.
The second value can be found from Wikipedia in (at least) two places.

The first Wikipedia occurence references the GSFC page--which is erroneous since that value does not occur there.
The second Wikipedia occurence references USNO's 2014 Astronomical Constants, which appear to themselves be copy-pasted from data in 2009 or 2012.  The second Wikipedia occurrence also sources NIST (presumably this table).  I couldn't find the cited mass from either reference.

The third (and also the fifth) value (which, it is interesting to note, are both outside the error bound given in the second Wikipedia occurrence) can be found on this generic NASA site.
The fourth value occurs in the book Handbook of Chemistry and Physics (Robert C. Weast, 1980)
The fifth value apparently also occurs in the book Astrophysical Data (Kenneth R. Lang, 1990ish).
The sixth value occurs in the book Physics--3rd Edition (Cutnell et al. 1995).  This site lists several of the values and does a calculation to obtain the sixth value.
Occurs in many places and is pretty clearly rounded.

The fifth, sixth, and seventh values (also) occur in various non-primary sources online, and I assume are rounded values of others.

My question: what is the most recent, best estimate, to the greatest precision, of the Sun's mass?  Obviously, citable, primary sources only!


texts: Does more ocean on an Earth analog produce a different rotation period?

texts: Would an exoplanet that has more ocean than Earth rotate at a different speed as a result of this? Would the amount of water impact the weight, gravitational pull, and/or tidal forces and cause a difference in the exoplanet's rotation period?  (For simplicity's sake, say, if it was earth-like in every respect other than having more ocean than Earth does at about 70% of the surface area.)


texts: Cosmology: about the equations of expansions

texts:
Suppose we assume that the gravitational constant is varying with time:
$$G=G_0 e^{-\frac{t}{t_0}}$$ where $t$ is the time from the Big Bang, and $G_0, t_0$ being some constants.

Assuming matter-only universe, which one of the expansion equation should we use to obtain the Hubble's parameter $H$?

Equation 1:

$$H^2=\left\{\frac{\dot R}{R}\right\}^2=\frac{8\pi G}{3}\rho_0\frac{R_0^3}{R^3}$$

Equation 2:

$$\frac{\partial (H^2R^2)}{\partial (R^2)}=\frac{\ddot R}{R}= -\frac{4\pi G}{3}\rho_0\frac{R_0^3}{R^3}$$


texts: What is the actual visual characteristics of a black hole?

texts:
Is there a safe distance in which a black hole can be observed with the human eye? What is a safe distance?

I have seen many computer simulated and artist renditions, and I am not sure if they depicted the true colors and shape of BH.

Below I have a few of examples of what may a BH may look like rendered.

How light from the accretion disk maybe refracted by gravitational lensing.
http://www.physics.utah.edu/~bromley/blackhole/index.html

https://www.bbc.com/news/science-environment-38937141

https://www.nasa.gov/connect/chat/black_hole_chat.html

Should these models be mixed to make a more complete rendition of a BH?


texts: Does a black hole necessarily contain a singularity?

texts:
I'm basing this hypothesis on the theories around how an outside observer watching something fall into a black hole will never actually see the thing pass the event horizon. And secondly that from the perspective of the thing falling in, the surrounding universe would accelerate to see the end of the universe.

On that second point, the "end of the universe" from my understanding would be up until the black hole evaporates.

So the question. Is it possible for an event horizon to form; not necessarily from a singularity, but merely from there being enough compressed mass existing within the boundaries that an event horizon forms?

The implication from this if it has any merit would be in my opinion, that there are no singularities currently in existence and that there indeed might never be one, because currently I don't understand how something "inside" a black hole is capable of moving at all (I assume that to do so mass would need to move faster than light), suggesting that the entirety of a stellar remnant's mass is stuck in place both inside and on the surface of the event horizon.

EDIT: Re-reading that last paragraph I've confused myself a little, mass wouldn't necessarily be "stuck", but if it did move at all, it would be moving light speed, which is a paradox in itself?


texts: How is it known that Pillars of Creation are destroyed?

texts: We can observe Pillars of Creation with 7000 years delay, but it is destroyed only 6000 years ago. How do we know that? How the information about explosion reached the Earth before light do?


texts: Does the summit of a small mountain offer better seeing?

texts:
I have a small amateur telescope, and would like to defeat the atmospheric seeing conditions as much as is possible.

Fortuitously, I happen to live fairly close to this lovely patch of bare elevated rock:

It's a granite peak about 3,155ft (960m) above sea level.

Would this peak be expected to have improved seeing, as compared to the seeing from an adjacent valley on the same night?


texts: South of the tropics, where does the sun's noon shadow point?

texts:
If I understand correctly, in countries to the north of the tropics the sun's noon shadow points north.

What happens south of the tropics? Is it pointing south?


texts: Why does the Moon seem larger when it is close to the horizon?

texts:
I've noticed that when I look into the sky at night, sometimes the moon appears very large near the horizon. Sometimes it also looks like it has a yellow tint.

Is this the light rays bouncing off the moon differently, or the atmosphere of the earth, or some type of sunspot blocking part of the light to the moon?


texts: Are satellites orbiting around earth visible to the naked eye?

texts: I was just lying under the sky trying to possibly see some meteorites, unfortunately never seeing any I might add, but I saw three objects all moving at about the same speed( all at different times). They were far too faint and small to be aircraft or anything inside of the atmosphere I would think and there were no blinking lights. They were also moving fairly quickly it seemed. Could these have been satellites in low earth orbit? It's the only other thing I would think that they could be.


texts: I need a way of to calculate the moon phase. Do you know resources for research the theory from behind this? I basically have searched in Google, but the results were not very satisfactory. Exists a mathematical formula for do this calculation?


texts: Any tip on maintaining a log of celestial objects?

texts: I am an amateur observer and Olympus 10x50 binocular is my tool. As I keep locating celestial objects (Planets, Stars etc), I would like to maintain a log of the observed objects. The purpose of the log is to list down the number of celestial objects I have observed/located. I need suggestion on what data points should I capture which helps in making some sense out of it and also encourage my friends to get into star gazing.


texts:
Time moves more slowly near a mass than in relatively empty space.  For example, I get that an observer would see someone falling into a black hole to appear to move more slowly and get "stuck" on the event horizon, while the falling body would see the observer as aging more rapidly.

Additionally, an observer watching a passenger craft moving near the speed of light (high mass equivalent) might see a passenger who tripped falling in slow motion, because the forward momentum of the passenger + the speed of the craft must never exceed the speed of light, while the passenger would experience no effect of this time dilation, and would simply trip and fall.

Which brings me to my question...

Black holes, even supermassive black holes, are nowhere near the mass of the universe as a whole; so when the universe itself was much smaller and far more dense, then at a universal scale time itself would have progressed more "slowly" than it does today, and since the expansion of the universe is accelerating, doesn't it mean that time is also accelerating?

(Assuming, of course, there was some "outside" to observe this from).

This is not a duplicate of Does time slow down because the universe is expanding at an accelerating rate?.  That question and its answers seem more concerned with local, relativistic time (which is as malleable as space itself).  My question asks more about the effect across a universal scale as it relates to density of mass across that same universal scale.


texts: Hypothetically, if our sun was yellow would we still see "white" colours?

texts: Hypothetically,if our sun was yellow would we still be able to see white colour on objects like snow,cotton etc.? Would we have the phenomenon of rainbow?


texts: Necessary steps to calculate photon's path by using null geodesic equation

texts: Can anyone please give me an explanation on how to calculate photon's path by using the null geodesic equation? N.B. I know all of the non-zero values of Christoffel symbols.


texts: So I just learned that CMB redshift is 1100 regardless where we look (up down left right). According to Hubble's Law that makes it around 46 billion light years away, making it the farthest matter away from us. If CMB redshift is the same regardless which direction we look, then how could that be unless we're in the center of the universe?


texts:
From my understanding, "up" and "down" in space is going towards (down) an object's gravitational pull or (up) which is going away from it. I get confused with this explanation, and I believe simply because of how we perceive up and down here on earth.

My question(s) is this: Can we go in all directions in space with the "Earth" interpretation of up, down, left, right, north west, south east, etc if we can get past gravitational pulls of objects in space?

Looking at my Gimp version of the universe, I have the Earth and stars. So going up would essentially be go towards any of the stars in the picture that has the strongest gravitational pull, although each object are on different planes?

In relation to my question above, I have imagined Earth in space as to like the 10 floor on an infinite elevator that can go in all directions. Say we can somehow go through star A and escape it's gravitational pull, we would be essentially "going down" right?

Now my other question: Are there objects in every single direction is space? How about in the Bootes void? Since it's such a massive void and there isn't much objects around to pull you in "down" or go away from "up", essentially can't we go in any direction?

If it may seems that my question about this is kind of confusing, I apologize because I'm confused about this myself!


texts: Why do the pulsations of a Cepheid variable occur?

texts:
I understand the theory of the mechanism by which Cepheid variables pulsate, where helium is ionised and deionised, leading to changes in diameter.
However, I am unsure if the brightness changes due to the changing opacity of helium, or is it explained by the changing diameter of the star, or perhaps a combination of both?
We learn through Stefan's Law that luminosity is directly proportional to the surface area. Is the changing surface area causing the changing luminosity, and this change in surface area is driven by the changes in helium ionisation? Or is the change in luminosity solely brought about by helium?
Thanks.


texts: Are any of the zodiac stars about to go supernova anytime soon?

texts: I have read that Betelgeuse, known as Ardra in Hindu astrology, could go supernova. Are any of the zodiac stars or the stars of lunar mansions about to become a black hole or supernova?


texts: What are the significant assumption of the Inflation Theory?

texts: Can it still be considered theory ?, because I can't find it's major or significant assumptions.


texts: How to calculate when the moon is highest in the sky to the earthbound observer?

texts: Like when is the new moon highest in the sky? Or third quarter? How do I know this for any general moon phase? Thanks.


texts: How many galaxies have had their distance determined using SNIa?

texts: Supernovae of type Ia can be used as standard candles to determine extra-galactic distances. But these event only occur (roughly) once every 200 years in any given galaxy and rapidly fade away. So to actually see a supernova in another galaxy, you have to be observing a lot of galaxies for a long time. This makes it seem like this isn't a very practical method to determine extra-galactic distances. To how many galaxies has the distance been determined using type Ia supernovae?


texts: Need help with the calculations/conversion of a celestial object

texts:
I'm developing a telescope controller open-source application. I started this project with a very little knowledge of Astronomy.
Basically, the app is going to send data to telescope over a wireless connection.

Data of the celestial object is as follow:

["SAO#": 308,
"HD": 8890,
"Con": "Alpha Ursae Minoris",
"StarName": "Polaris",
"RAH": 2,
"RAM": 31.812,
"DED": 89,
"DEM": 15.85,
"Mag": 2.02,
"PRA": 0.038,
"PDec": -0.015]

RAH = RA hours, RAM = RA minutes,
DED = Dec degrees, DEM = Dec minutes

(PRA and PDec are the drift of the star in arc-seconds per year (from the catalog Epoch J2000.0). I don't need to use these in the app, that I'm told.)

The controller server (data receiver) accepts in this format:
Set target RA- HH:MM:SS,
Set target Dec- DD:MM:SS,
Set target Azm- DDD:MM:SS,
Set target Alt- DD:MM:SS

I would want to convert the given celestial object data to Ra, Dec, Azm, Alt.

I'm told that:

RA = ((RAH + (RAM / 60.0)) * 15.0); //in degrees, RA is an earthly longitude projected onto the sky
DEC = (DED + (DEM / 60.0)); //in degrees, Dec is an earthly latitude projected onto the sky

For a star or other celestial object from the catalogs they have a fixed Epoch (J2000.)  I need to apply a correction for precession/nutation (wobble of the Earth's axis of rotation) to get a half decent estimate of the star's RA/Dec "now".

I'm using a code library that seems to have support for this and does the calculation on it own.
I would want to know the procedure of the data conversion from equatorial coordinates to horizontal including.
For an instance this is how the code works:

    let jd = Date().julianDay
    let RAH = 2.0
    let RAM = 31.812
    let DED = 89.0
    let DEM = 15.85

    let eqCoor = EquatorialCoordinates.init(rightAscension: Hour((RAH+(RAM/60.0))*15.0), declination: (Degree(DED+(DEM/60.0))), epoch: Epoch.J2000, equinox: Equinox.standardJ2000)
    let annualAbb = eqCoor.correctedForAnnualAberration(julianDay: jd, highPrecision: true)
    let initEQ = AstronomicalObject.init(name: "Polaris", coordinates: annualAbb, julianDay: jd, highPrecision: true)
    print("EquatorialCoordinates -> RA(α):", initEQ.equatorialCoordinates.alpha, "DEC(δ):", initEQ.equatorialCoordinates.delta)

    let userLocation = GeographicCoordinates(positivelyWestwardLongitude: Degree(.plus, 75, 51, 13.65), latitude: Degree(.plus, 30, 54, 43.55), altitude: 256)
    print("User Location -> Latitude:", userLocation.latitude, "Longitude:", userLocation.longitude)

    let preccCoor = annualAbb.precessedCoordinates(to: Equinox.standardJ2000)
    let horizontalCoor = preccCoor.makeHorizontalCoordinates(for: userLocation, at: jd)
    print("Horizontal Coordinates -> Azimuth:", horizontalCoor.azimuth.inHours, "Altitude:", horizontalCoor.altitude.inRadians.inDegrees)

This is the data that code returns:

EquatorialCoordinates -> RA(α): +37h56m06.009s DEC(δ): +89°16'05.165"
User Location -> Latitude: +30°54'43.550" Longitude: +75°51'13.650"
Horizontal Coordinates -> Azimuth: +12h1m07.396s Altitude: +30°13'16.650"

Here's the data from Stellarium according to the same location as my code.

The data calculated from my code is not even close to the one from Stellarium except apparent altitude.


texts: Data on galactocentric distances of various stars?

texts: I'm creating a project for my astronomy class (introductory course) that requires knowledge of the galactocentric distances for many stars. I'm struggling to find a good source on this, and I'd rather not parse through dozens of papers to compile it myself if possible. Is there a good table of stars (preferably around 100 or so) that includes their galactocentric distances? (Obviously you could calculate it using galactic coordinates but that's too complicated for my students to do for several stars)


texts: What does the opacity of a molecular transition mean?

texts: In particular, what does it mean when a line (e.g, emission line in stellar wind) is optically thick or thin. I know what an optically think/thick medium is, but how does this concept compare to optically thick/thin line.


texts: What differentiates a "group of rogue stars" from a galaxy?

texts:
According to Wikipedia, a rogue star or intergalactic star is

  not gravitationally bound to a galaxy.

But according to a citation on the same Wikipedia page, the first intergalactic stars were discovered in the Virgo cluster of galaxies.

  These stars form a massive group  aproximately 300,000 light years away from the nearest galaxy. (Emphasis mine)

Is there any clear, stated definition which differentiates galaxies from "massive groups of rogue stars"?


texts: Telescope focal length, reducer and/or Barlow

texts:
Say I have a scope with a given diameter $D$, a given focal length $f$, and a given exit barrel diameter $B$. It has a maximum true FoV of $B/f$ (supposing $B<<f$).

Would adding a 0.5x focal reducer exactly amount to having a $D/(f/2)$ scope with barrel size $B$, for all intends and purposes (i.e. be optically indistinguishable from an actual scope of diameter $D$ and $f/2$ focal length) ? I feel like it should, but I'm unsure whether maximum true FoV would indeed become $2B/f$ as on a "natural" $D/(f/2)$ scope.

(You may ignore light absorption from the focal reducer' lens(es))

Conversely, say I have the same initial scope with a given diameter $D$, a given focal length $f$, and a given exit barrel diameter $B$ (it still has a maximum true FoV of $B/f$ (supposing $B<<f$)).

Would adding a 2x Barlow exactly amount to having a $D/(2f)$ scope with barrel size $B$, for all intends and purposes (i.e. be optically indistinguishable from an actual scope of diameter $D$ and $2f$ focal length) ?


texts:
I have a problem: If I would dig a hole through the earth, and jump right in, disregarding the rotation of the earth, I should come back out on the other side.

However, orbital mechanics say otherwise: Specific Orbital Energy tells me:

v^2/2 - µ/r = -µ/2a

Now, on the planet, my relative velocity is 0 m/s, so v^2/2 = 0. The term simplifies to:

-µ/r = -µ/2a | / (-µ)
1/r = 1/2a | ^(-1)
r = 2a | /2
a = r/2

My apoapsis is 3000 km by this equation. But it should be 6000 km, since I come out of the other side.

Why is this, and did I do a wrong assumption?


texts: Resource Recommendations to systematically develop a foundation via Self study in Astrophysics/Astronomy?

texts:
I am a high school senior (Grade 12) with a passion for Astronomy/Astrophysics. I already searched quite a bit here on the other questions on resources, but I couldn't find any that shows a concise, systematic order that one can follow. (I might have also missed it if so I do apologize. If it helps I do have quite a decent handle on AP-level Calculus and decent physics background.
So, I would like a systematic order of books, videos, resources of any kind that I could peruse to achieve a significant foundation (and ambitiously say up to a Graduate level?) in Astronomy/Astrophysics.
Thank You!!!


texts:
A year is measured as the amount of time it takes Earth to orbit the Sun once, a Galactic year is the time it takes our sun to make one full orbit of the center of the Galaxy.

In Galactic years, how old is our Sun?


texts: death of a red dwarf star / minimum mass needed for a white dwarf?

texts:
OK, first, I know there's a variety of sizes and types of red dwarf stars and the universe is too young for any of them to have reached the end of their main sequence phase yet, so it's all theoretical and/or modeling.
http://en.wikipedia.org/wiki/Red_dwarf
But what is the theoretical size needed for a star to undergo the electron degeneracy process which turns a small star from at least Jupiter sized, usually bigger, into to earth sized super dense object, where, as I understand it, the electrons are squeezed off the nuclei - electron degeneracy.
It would seem to me that a 7.5% solar mass star, which gradually burns hydrogen into helium but doesn't burn helium, might not have the mass to compact into a true white dwarf but might end it's life looking more like a brown dwarf / super Jupiter - well, talking appearance, not really, because super Jupiter & Brown dwarfs are mostly hydrogen while and an end of life red dwarf should be mostly helium - which, in and of itself, might make the difference.
It's just my curiosity whether all red dwarfs turn into white dwarfs at the end of their burning phase or is there a theoretical mass that's needed for that level of shrinkage to occur?
Thanks.


texts:
Disclaimer: I’m not a career astronomer.  I don’t own a telescope.  I have no professional credentials.  But I do find this stuff fascinating, and I consume all the astronomy documentaries I can.

So, I’ve watched lots of documentaries describing stellar evolution.  I understand that below a certain threshold, stellar death does not involve supernovae.  I understand that above that threshold, supernovae may create neutron stars, magnetars, or (if the supernova qualifies as a hypernova) black holes.

However, for a long time, I was curious about why stars below the supernova threshold—like our own Sun—become Red Giants.

From documentaries, I have been instructed that (for stars below the supernova threshold), when the star’s core’s fusion cannot continue…fusion ceases, and the star begins to collapse under gravity.

As gravity crushes the star, I understand that the star heats up as gravity crushes it.  As a result, although the stellar core remains “dead” (no fusion occurs), a “shell” of gas around the stellar core becomes hot enough to begin fusing helium.  Since the fusion occurs as a “shell” around the stellar core, the outward-push from the fusion is what pushes the star’s outer layers further.  The result is that the star grows into a Red Giant.

My question is this:  Why does fusion cease in the core?!  It seems to me that as gravity crushes the star, stellar fusion would reignite in the core itself—not in a sphere around the core.  Why does the stellar core remain “dead” while its “shell” begins fusion???


texts:
I got a cheap refractor as a present - my intro to astronomy. I think it’s not great, but I’m having plenty of fun looking at the moon and planets, and who knows, maybe some other objects soon.
The thing that limits me the most, I think, is the tripod that came with it. It is super flimsy, I can hardly point it at the right thing, even focusing the telescope moves the alignment. It’s also too short, so I’m hunching down all the time.
I’m therefore wondering, might it make sense to upgrade just the mount for now? If I end up taking it up as a hobby, I can maybe upgrade the telescope, and if not, it’s less money than buying a “proper” set. Just a simple alt-az probably, but dedicated to astronomy. The refractor is super light so doesn’t need anything fancy.
Due to life situation, I’m not really in a position to join a club and explore this way, I can do my astronomy when I have 15 minutes to spare (and a clear sky!).


texts:
Electrons annihilate with positrons produced through fusion processes in stars. Which particle interaction produces new electrons so that the sun isn't deplete of electrons? Or is something else happening altogether?

Regular fusion cycles in stars produce neutrinos and positrons as by products. Those positrons annihilate with electrons that are already there in the plasma of the star to produce the light that we eventually see. How are those electrons replaced?


texts: Intrasolar planetary surface temperature change divergence from Earth

texts:
Considering the vast amount of insulating gas emitted by human activity on Earth without a coincident release on all other planets in the solar system as well as the phenomenon that planets in a solar system normally exhibit similar coincident temperature changes described here, how far have temperature changes diverged from Earth's?

Please include raw data, graphed if possible.


texts: Is there a general term used to identify the high flat features within Noctis Labyrinthus on Mars?

texts:
At the western end of Valles Marineris, where it mets Noctis Labyrinthus (highlighted section of image)

there are a series of flat geological formations between the canyons.

Is there a unique term for these formations, or even one borrowed from Earth's geology?

Has the individual sections of these formations been named?


texts:
I live in western Saudi Arabia, I am trying to see the comet ISON, reading here and there tells that I can see it by naked eye somewhere next to the constellation leo, I used an app to tells me where constellation leo is but I could not see the comet.

Is it visible from Saudi Arabia? if so, in which direction (west, east, etc.) and what time is the best to see it?


texts: Looking for planetary position calculation

texts: In Hindu astrology, for creating horoscopes (birth charts), I am looking for calculations of planetary positions. So, how could I calculate planetary positions according to given date, time and place?


texts: All the solar system simulations I've come across showing the positions of planets only show the positions in a certain time period, at beginning of the first millenium the earliest. There was just one exception where I could enter minus-years but it's unreliable (and in fact there never was a year 0). Do you know a simulation/planetary system map where I can learn the planet's positions before Christ? To make it clear: I mean the planet's heliocentric positions (when you look on our system from 'above' the Sun), not their location on the sky.


texts: Rings around a smaller, close-in planet?

texts:
Is it possible for a small, close-to-star planet to have a stable ring system--icy or otherwise?

A smaller planet means the rings would have to be closer to the planet, which means the radial shear (difference in orbital speed vs. radius) in the rings would be higher. A higher radial sheer would be more likely to cause turbulence...or so I would think.

Obviously one would not expect icy rings around a planet that's inside the frost line....


texts: Not clear on how to calculate sub-radar latitude

texts: How to find sub-radar latitude in reference to radar telescopes hitting near earth asteroids?


texts: Radiation and software reliability in outer space

texts: We all know that dragon was written in c++ but what i struggle to understand is that if radiation in space can really mess with hardware and functionality and even have the capacity to change bits from 0 to 1 or vice versa how is that mitigated? Do you put wall of lead around the critical hardware?


texts: Knowing the RA/DEC of a star how do I locate a star from ground?

texts: Standing in Melbourne at 4 am in the morning on 14th April 2019,  Sirus RA = 06h 45m 08.9s, Dec = -16° 42' 58"..How do I Locate this. Standing facing east I turn myself towards south approx 90 Deg and then look up about 16 Deg, I do not find any star.


texts: Why more matter still left after collision with anti-matter?

texts: Question implies all, why is that? Why we exist even after equally creation of matter and anti-matter, any possible exception?


texts: Does time slow down because the universe is expanding at an accelerating rate?

texts:
If the universe is expanding at an accelerating rate, such that the galaxies' moving away from each other is accelerated, then time should also slow down.
And when universe will accelerate to the speed of light, then time should stop.

Does time slow down because universe is expanding at an accelerating rate?
Can any physicist explains if this is true or not?


texts: Can hawking radiation be eaten by another blackhole?

texts:
Just a theory, from this video. At last, only the black holes are gonna exist and even they'll decay because of hawkings radiation.

As black holes emit hawkings radiation, then if one emits it, another should absorb it, this will create infinite loop kind of thing & universe is never gonna be empty as blackholes will keep on refilling!

Question: Can a black hole absorb hawkings radiation from another black hole?

(this question is quite obvious if we think that black holes can absorb anything but how's that gonna make the universe empty)


texts: Does exist something like a distribution of number of galaxies per redshift interval? I'm studying galaxy formation and evolution, and I'm curious to know how many todays' galaxies (with redshift <0.01 I would say) we see.


texts: Was the Geocentric Model correct at all?

texts:
It's easy to find resources stating that the heliocentric model is right and geocentric is wrong.
But how wrong was it? Was it correct in any way?
It was built on incorrect assumptions, but despite that - was it of any use to describe the apparent motion of celestial bodies? Was it more accurate for some things, but less accurate for others? Or was it altogether a flop and astronomers couldn't get anything out of it either way?

I can only find multiple articles proving the heliocentric model, explaining the geocentric one or claiming that it was simply wrong - but I can't find anything about its accuracy and usefulness.
(1) (2) (3)

Edit 1:
I incorrectly used geocentric model when it seems I wanted to say Ptolemaic model - the one with deferents and epicycles, with Earth as its origin.

Ptolemaic model (click for full size)

Thank you for clarifying, and sorry for the confusion. The answers provided regarding any other geocentric models are still valid and useful, so this is just a minor errata.


texts: Why was Uranus named what it was, and who came up with the name?


texts: How do we know distant stars still exist

texts: The Pleiades are 450 light years away. Thus when we see the twinkle in the night sky the light that hits our retina emanates from the year 1569 or so. On that proviso; how can we be sure that the star is still alive given the fact that we are seeing light from hundreds of years ago.


texts: How does the ITRS frame related to ECEF frame?

texts: How does the International Terrestrial Reference frame related to the Earth-centered, Earth-fixed frame, as both of them rotate with the Earth?


texts: How do rogue planets orbit around stars in other planetary systems?

texts:
I got some interesting answers for What would happen if a rogue planet hit one of the planets in our Solar System?

But I have seen some documentaries that state that rogue planets from other planetary systems (which are ejected from the planetary systems in which they formed) have become part of the other planetary systems and orbit around those new stars as planets.

For example, please check this link:

  The latest research suggests that sometimes, these rogue, nomadic worlds can find a new home by being captured into orbit around other stars.

How is this possible? Stars' gravity can pull the rogue planet into them. How do rogue planets escape this and orbit around the new stars. This seems to be a bit mysterious.


texts: Why do pulsars turn "off" from rotation?

texts:
I was looking at a wikipedia article (https://en.wikipedia.org/wiki/Pulsar#Formation,_mechanism,_turn_off)
and I came across an interesting aspect that said pulsars turn off from rotation. What I don't understand is why emission of EM waves would slow a pulsar down?


texts: Time-density and time-temperature functions of the Universe since the Big Bang

texts:
I am looking for these... functions. I want to be able to say, "at a 1873. second there were around 54230000000 K temperature and 0.00435 kg/m^3 density".

On the net I could find only tables or diagrams, as this: .

(Here is a link to the page it accompanies: http://www.astro.ucla.edu/~wright/BBhistory)

I am practically interested in the interval between the first seconds and the first some ten millions of years.

Is it possible? Some simple formula were also enough (although I think, there are different formulas for the different eras after the Big Bang).


texts:
What are the most popular packages used to create graphs for astronomy journal papers?
Looking at various journals, the styles of the graphs appear to be quite uniform but I can't identify the package(s) that create them.


texts: What's the highest frequency that's been imaged by a radio telescope?

texts:
In this answer to Should we update definitions and remove the 100 GHz hard limits on radio astronomy related tags? I wrote the following partial answer:

Yes, there are plenty of dishes that focus into waveguides or horns that feed antennas connected to electronic amplifiers using transistor amplifiers connected to heterodyne down-conversion with balanced mixers and then analog-to-digital conversion, where intensity images are produced by interference implemented mathematically in a computer (rather than in wavefronts incident on material producing intensity signals in the form of electrons (CCDs) or phonons (bolometers)) which work up to circa 1,000 GHz, so the 100 GHz limit is obviously wrong!

With the idea in mind that a radio telescope might be defined as using conversion to electrical signals before conversion from amplitude to intensity (image formation), what's the highest frequency where this has been done?
One number I know is 230 GHz, which was used by the Event Horizon Telescope

The question How does ALMA produce stable, mutually coherent ~THz local oscillators for all of their dishes? suggests this is at least 950 GHz, but I don't know if that's a record or not. Narrow band optical emission could be mixed with a laser in a nonlinear crystal producing a microwave signal that could be detected via radio, so potentially the answer might be visible or near infrared light, but I don't know.
update: So I've gone ahead and asked this separately: Has optical interferometry been done at radio frequency using heterodyning with a laser in a nonlinear material?


texts: How do I reduce planetary photometry to standard viewing geometry using phase angle?

texts:
I'm trying to make light curves for Pluto using old data. Most papers give magnitudes "reduced to standard viewing geometry" of r = 39.5 AU, Δ = 38.5 AU, and α = 1 degree, where r is heliocentric distance, Δ is geocentric distance, and α is phase angle.

When papers give apparent magnitudes, I'm left to perform the reductions myself. I'm fine with the adjustment for r and Δ, but how do I reduce to phase angle of 1 degree?

I would also really appreciate a good source if you have it on hand.


texts: Horizontal to Equatorial Conversion - Code

texts:
Following this tutorial I have been able to convert from Equatorial to Horizontal Coordinates and am now searching for a way to do the reverse.
I understand this kind of question has been asked and answered using mathematics, but I have been unsuccessful in implementing the provided algorithm in code. Below is my C Sharp code for Equatorial -> Horizontal conversion, which I'm looking to reverse.
public static HorizontalCoords EquatorialToHorizontal(EquitorialCoords equatorialCoords, GeographicCoords geographicCoords, double localSiderealTime)
{

    double ha = (localSiderealTime - equatorialCoords.rightAscention) * hours2deg;

    double x_sid = Cos_d(ha) * Cos_d(equatorialCoords.declination);
    double y_sid = Sin_d(ha) * Cos_d(equatorialCoords.declination);
    double z_sid = Sin_d(equatorialCoords.declination);

    double x_hor = x_sid * Sin_d(geographicCoords.latitude) - z_sid * Cos_d(geographicCoords.latitude);
    double y_hor = y_sid;
    double z_hor = x_sid * Cos_d(geographicCoords.latitude) + z_sid * Sin_d(geographicCoords.latitude);

    double az = Atan2_d(y_hor, x_hor) + 180;
    double alt = Atan2_d(z_hor, Sqrt(x_hor * x_hor + y_hor * y_hor));

    return new HorizontalCoords(alt, az);
}

public static EquatorialCoords HorizontalToEquatorial(HorizontalCoords horizontalCoords, GeographicCoords geographicCoords, double localSiderealTime)
{
  //*hmmmmmm what goes here..
}


texts: Is there a way to calculate how much damage black hole merger shockwaves inflict on nearby objects?

texts:
Black hole mergers lose respective rotational energy during a merger. I understand that the energy 'emitted' is scattered as gravitational 'energy' that can henceforth be detected by gravitational detectors billions of light years away. I understand that the amount of shockwave energy in stellar mass black hole mergers can be equivalent to the mass of a star such as the sun. So if two rapidly rotating SMBHs on the scale of SagA* merge, the emergy emitted is in the range of hundred thousands of solar masses...?

Either case that is a lot of energy. If a two, let's say, 10 solar mass black holes merge at 10 light years, what are the literal impact effects on a terrestrial planet in such adjacent system?

Barely sensable by its inhabitants? Significant seismic? sufficient to sharply increase volcanism? Agitating the surface to lava? Obliterate small moons or planets in to a large rapidly expanding cloud of interplanetary lahar?

Assume that every ten thousand or less years such merger occurs in the milky way galaxy? Could these mergers constitute existential risks?


texts:
What are the white reflections on Ceres?

https://solarsystem.nasa.gov/planets/dwarf-planets/ceres/overview/


texts:
I've tried utilizing "Google Sky", however, once I've found the location of said star and am in the process of zooming in, the site craps out.
Anyway... if there's someone out there with a little more experience in this field, here are the coordinates of the star i'm searching for:
10h 10m 11.1s, +4 3' 12.3"

I'd appreciate the effort, and thank's in advance.


texts: Could the mineral composition of planets explain the absence of megastructures?

texts:
The Fermi paradox concerns why we don't observe evidence of alien life, such as megastructures. If we were to build a Dyson swarm, the best source material may be Mercury (Armstrong and Sandberg 2013): not only is it close, with plenty of solar power for exponential disassembly, but its mineral composition is suitable. But could planets made of suitable minerals, with plenty of solar power, be rare enough to prevent most advanced civilizations building Dyson spheres, or other detectable megastructures?

It's a mundane solution to the Fermi paradox, but it's conceivable on my limited knowledge of exoplanets, if only because our planetary system is atypical. For example, where we have Mercury, many systems would have hot Jupiters instead (or possibly as well, if that's consistent with how most systems form). Can we begin to answer this with our current understanding of what's typical for exoplanets?


texts: I have a question about iron stars. I was fascinated about the theory about the inability of protons to decay, and it led me to a point where I read something about some special kind of star called an "iron star". Can anybody enlighten me a bit, if possible, on what exactly it is and why it may be significant? And how do iron stars form?


texts: When Phobos collides with mars (or breaks up), will it have any noticeable effects on Earth?

texts: When Phobos meets its predicted doom in a few 10s of millions of years, whether it breaks up or collides with the surface of Mars, will this change have any noticeable effects (permanent or temporary) on the Earth?


texts:
This comes from a comment on this question, to quote:

  The death of (large mass) stars is also based on quantum events with probabilities technically not 1 (and is very fast), so it is technically possible for a star not to die in a way it really ought to by sheer chance.

The question is what quantum events are involved in the death of a star (likely and unlikely)? If many of these very unlikely quantum events happened at the same time all over the star, how could the death of a star differ form the typical nova or simply cooling down?


texts: What is the formula to figure out how far away a star is?

texts:
I have tried to search for this but it won't show me the formula or "how to" figure out the formula. So what is the formula, and how do you figure it out?

(The formula for stars within 400 light years.)


texts: What is the period of the 'cycle' of Earth's ecliptic variation, relative to the 'invariable plane'? 70,000 or 100,000 years?

texts:
The plane of Earth's path around the Sun, the ecliptic, is different from the average of the solar system's as a whole (the invariable plane) by about 1.57°....
Our path around the Sun, though, goes through a periodic variation, tilting up and down, over a period of many years... But how many?
From Wikipedia:

The inclination of Earth's orbit drifts up and down relative to its present orbit. This three-dimensional movement is known as "precession of the ecliptic" or "planetary precession". Earth's current inclination relative to the invariable plane (the plane that represents the angular momentum of the Solar System, approximately the orbital plane of Jupiter) is 1.57°.
Milankovitch did not study planetary precession. It was discovered more recently and measured, relative to Earth's orbit, to have a period of about 70,000 years. However, when measured independently of Earth's orbit, but relative to the invariable plane, precession has a period of about 100,000 years. This period is very similar to the 100,000-year eccentricity period. Both periods closely match the 100,000-year pattern of glacial events. [6]

Huh?
Is it 70,000 years or 100,000?


texts:
So, I am learning about quantum entanglement in my quantum course and had a thought. If the Big Bang is the creation of everything - time included, and this came from a single "source". Would it not follow that all particles in the universe are entangled to each other? And perhaps, we cannot observe this entanglement because we are "inside the system" sort to speak. Are we not all connected?

I know the last part is cheesy, but the point is serious.


texts: How is the first detonation in Supernove type Ia triggered?

texts:
Ok, I read about the Supernova of type Ia and I found out that there are two detonations happening. First one is in helium shell around the white dwarf and second one seems to be triggered by the first one and it is the main part of whole supernova. I did not find how this helium shell explodes at all so that`s what I am looking for.
Thanks in advance!


texts: Has optical interferometry been done at radio frequency using heterodyning with a laser in a nonlinear material?

texts:
If one collects narrow band optical emission from a large telescope with frequency $f_1$ and mixes it in a nonlinear crystal with laser light of a nearby frequency $f_2$, it would produce two new signals at $|f_1+f_2|$ and  $|f_1-f_2|$.
The difference signal $|f_1-f_2|$ could be picked up electromagnetically or perhaps it would be detectable as an AC component in a photodetector somehow, perhaps the photodetector would be the nonlinear element itself.
Once the signal is electrical, it could be recorded for later playback and offline interferometry, or for transmission over large distances for large baseline optical interferometry, or both.
Is this "a thing"? Has anything like this been done or at least tried?


texts: On the lack of observational records by European astronomers of the 1054 guest star

texts:
This question relates to the Crab nebula, the Crab Pulsar and the known concurrent supernovae event as recorded by Chinese astronomers in 1054.

I'm wondering, I'm looking at the history of the discovery of the Crab pulsar...and I'm wondering what the reason is (or suspected to be) as to why European records show a discernible lack of observations?


texts: How does Ptolemy prove in the following excerpt that the Earth could not be outside of the axis spanning between the poles of the celestial sphere

texts:
I have trouble interpreting the following excerpt:

  “Against the first of these three positions militate the following arguments. If we imagined [the earth] removed towards the zenith or the nadir of some observer, then, if he were at sphaera recta, he would never experience equinox, since the horizon would always divide the heavens into two unequal parts, one above and one below the earth…”

For context, when Ptolemy is speaking about “the first of these three positions…” he’s speaking about the position that holds that the Earth is equidistant from both poles of the celestial sphere, but is not on the axis spanning between both poles.

He states that he’s arguing against the first proposition, and suggests that if an observer were at sphaera recta (which I’ve taken to mean that the observer is at the equator with direction/horizon being perpendicular to the equator,) then he would never experience equinox because his “horizon would always divide the heavens into two unequal parts, one above and one below the earth…”

I assume that in this case, while the Earth is displaced from the center of the celestial sphere, the Sun is still orbiting the true center. However, if it was equinox, and the Sun was orbiting on the same plane as the true center. Wouldn’t this observer still experience equinox because the Earth is still on the same plane as the true center?

Here’s the link to my source (page 41, chapter 6:) https://isidore.co/calibre/get/pdf/Ptolemy%26%2339%3Bs%20Almagest%20-%20Ptolemy%2C%20Claudius%20%26amp%3B%20Toomer%2C%20G.%20J__5114.pdf


texts: Can singularities not hidden behind an event horizon, known as "naked singularities", arise from realistic initial conditions, or is it possible to prove some version of the "cosmic censorship hypothesis" of Roger Penrose which proposes that this is impossible? Similarly, will the closed timelike curves which arise in some solutions to the equations of general relativity (and which imply the possibility of backwards time travel) be ruled out by a theory of quantum gravity which unites general relativity with quantum mechanics, as suggested by the "chronology protection conjecture" of Stephen Hawking?


texts: Does Triton trigger the active atmosphere of Neptune?

texts: As we know the atmosphere of Neptune looks more active than Uranus', is this due to the tidal forces caused by the retrograde orbit of Triton around the planet?


texts: Were effects of a planetary magnetic field reversal observed on other planets than Earth?

texts:
From geological records in rocks and minerals we know that the magnetic field of Earth changed its polarity multiple times in the history. See Geomagnetic reversal.

Was a similar process of a planetary magnetic field reversal observed on other planets?

I suppose that the record could be in rocks directly found on the planet (i.e. Mars), on its moons or in asteroids.


texts:
The abstract of Gravitational waves from mountains in newly born millisecond magnetars says:

In this paper we study the spin-evolution and gravitational-wave luminosity of a newly born millisecond magnetar, formed either after the collapse of a massive star or after the merger of two neutron stars. In both cases we consider the effect of fallback accretion, and consider the evolution of the system due to the different torques acting on the star, namely the spin up torque due to accretion and spin-down torques due to magnetic dipole radiation, neutrino emission, and gravitational wave emission linked to the formation of a `mountain' on the accretion poles. Initially the spin period is mostly affected by the dipole radiation, but at later times accretion spin the star up rapidly. We find that a magnetar formed after the collapse of a massive star can accrete up to 1 $M_{\odot}$ , and survive on the order of 50 s before collapsing to a black hole. The gravitational wave strain, for an object located at 1 Mpc, is $h_c \sim 10^{-23}$ at kHz frequencies, making this a potential target for next generation ground based detectors. A magnetar formed after a binary neutron star merger, on the other hand, accretes at the most 0.2 $M_{\odot}$, and emits gravitational waves with a lower maximum strain of the order of $h_c \sim 10^{-24}$ , but also survives for much longer times, and may possibly be associated with the X-ray plateau observed in the light curve of a number of short gamma-ray burst.

Question: What would a kHz gravitational wave detector look like? (mountains on millisecond magnetars) How would it differ from LIGO/Virgo?

Figure 1. Pictorial description of the millisecond magnetar. There are two coordinate systems, one having the rotation axis ($\Omega$) and another having the magnetic moment ($\overrightarrow{\mu}$) axis. These axes are inclined at an angle $\alpha(t)$. The blue dots show matter falling on the two polar caps and forming two accreting columns. As the star rotates, it radiates energy in dipolar radiation and grav- itational waves. The red dotted lines represent the escaping neutrinos which carry away heat and angular momentum in the form of a wind.


texts: Slow moving, flashing star-like object in the sky. What could it be?

texts: The sky was particularly clear last night and I noticed an extremely bright star. I thought it was venus possibly but it was too low down and was flickering craziy. That meant that it couldn't be a sattelite because they don't emit their own flashing light. So I just left it, assuming it was a close star. Then when I looked up at around 9 it had shifted to the right. I know stars move but it had only been about 30 minute since I'd last checked and it had moved across my vision. So it wasn't fast enough to be a meteor or sattelite etc but definitely wasn't a star because it was visibly moving and i tracked it throughout the night as it got lower and moved east. By 10pm it had moved all the way to the edge of my vision, I had to crane my neck to see it from the window. I had also been tracking the other stars just to check the rate at which they were moving. Orion's belt had moved a little (as expected) but obviously not as fast as this object. They were both moving in the same direction east but the object was also moving significantly south, therefore unaligned with anything I could see. After some researching I have concluded that it could have been sirius, the brightest star, south-west of Orion's belt but I'm just not believing that it would have moved that fast. So ultimately I'm sure it isn't something too whacky but are there any other explanations? :)


texts: Why moon sighted only in Kerala but not in rest of India?

texts:
I know for most of you the question may look silly, but Kerala is a state in India where the moon (Ramadan moon) will be sighted but not in rest of India.

I was reading the news article where I got a little hint but was not clear for me since I am newbie, tried to google but couldn't find much info :) can someone explain me.

  Eid is likely to be celebrated in Kerala tomorrow. Due to the
  geographical location of the coastal state, the lunar moon is sighted
  in the state a day before the rest of India.

Here is the article link Moon sighted in Kerala


texts: Ramifications of black hole stellar system

texts:
Recently, I got around to seeing the movie Interstellar. In it, the characters of the movie visit a stellar system that appears to be built around a black hole instead of a star. On top of this, their mission is to find a habitable planet in this system. Question: I was wondering how stable the system, as a whole, would be in terms of operation and would any of the planets be habitable at all due to the obvious differences between a star and a black hole.
In the movie the black hole is supposed to be a 'supermassive rotating black hole'. As for being a binary star system, it's never stated as such nor depicted as such. It's depicted visually as the black hole alone being the center. However one of the characters does mention a "Neutron Star" as part of the system so it could possibly be a binary star system. The ambient lighting for the planets is generated by the accretion disk of the black hole. The size and rotation speed of the event horizon are not defined in the movie. At least not that I can remember.
As for the planets, their proximity varies, with the first planet depicted as being so close to the event horizon that it is effected by time dilation. The distances of the other two are not specified directly, but traveling to the second planet out seemingly takes days, while traveling to the third planet out is stated to take months, if I remember correctly. As for their surface gravity, the first planet is depicted as having higher surface gravity than Earth but not so much higher that movement is impossible, just strained. The second planet is depicted as being '80% Earth's gravity', if memory serves me correctly.
To better help define certain variables relevant to the question I found an info-graphic related to the movie that illustrates the size of the black hole and it's rotational speed: http://tinyurl.com/pqph8wl


texts: Does Mars contain more iron than the Earth?

texts:
Is the reason Mars is red because its surface contains a lot of iron? (When dirt is red on Earth, it is sometimes caused by a high amount of iron).

If so, does Mars contain more iron than the earth?


texts: Has the velocity of photons coming from black holes already been measured?

texts:
Has the velocity of photons, which are coming from black holes, already been measured? I am not aware of such measurements.

The reason for the question is the following: If space-time near black holes has some extra dimensions, than photons created in this higher dimensional space-time might have non-zero components of the wave-vector in these extra dimensions. On the earth however we see just our 3 or 4 components of the wave-vector, so we might see just the projection of the original wave-vector onto our (3,1)-dimensional space-time. In this case the velocity of the photons might be less than the standard velocity of light.

I have in mind a special model of our universe. I believe, that our universe is the horizon of a (4,2)-dimensional space-time. On this horizon (which is our universe) we do not see the extra dimensions, however, they should be visible near black holes. So, in this model, black holes are the windows into the extra dimensions.


texts: Are Gamma Ray Bursts of galactic or extragalactic origin?

texts: I read about the 1995 Lamb-Paczynski debate on whether GRBs are galactic or extragalactic in origin.  With our current experimental evidence, have we found whether GRBs are galactic or extragalactic?


texts: Strength of gravity during the big bang?

texts: I was watching a documentary on the big bang, one of the astronomers said that initially the four fundamental forces were combined as one, they then emerged to become: The strong and weak nuclear forces, the electromagnetic force and the gravitational force. He claimed that the first force to emerge was the gravitational force, he went on to say that had the gravitational force been weaker than it is everything would fly apart so no galaxies would form and if gravity was too large than we would end up with black holes everywhere, so the force of gravity needed to be just right, as it is now. I couldn't find anything backing up this information online or the reasoning behind this information, any help would be appreciated.


texts:
Caught a sight of moon tonight (by chance) and came in surprise that moon looks thrice in size to its usual size.

Mostly called as Blue moon. Didn't succeed in getting the details and explanations of the phenomenon on Internet. Wikipedia just tells about the origin of the word blue moon and particular dates at which super moon is more obvious but doesn't shed the light on the true physical causes.

Just wondering what could be the causes that makes the appearance of moon (near the horizon) so big.


texts: What's the equation for moon-moon tidal heating?

texts:
Between a moon and the primary, the equation for tidal heating is:
$$\dot E_\mathit{Tidal} = - Im(k_2) \frac{21}{2} \frac{GM_h^2 R^5 n e^2}{a^6}$$
But how does one calculate the tidal heating between moons?
Simplifying assumptions I'm fine with:

The moons are coplanar, $I_\mathit{affected} = I_\mathit{perturbing} = 0$
Both orbits have no eccentricity, $e_\mathit{affected} = e_\mathit{perturbing} = 0$ (which also implies no heating from the primary)
The affected moon is tidally locked to the primary
The perturbing moon can be treated as a point mass

While I'm not able to come up with any formula, I suspect the following properties hold:

The tidal heating is still proportional to $Im(k_2)$, as this seems to only be an internal property of the moon.
It's still proportional to $R^5$
Since tidal forces are inversely proportional to distance cubed, I think the overall heating is proportional to ${(a_\mathit{affected} - a_\mathit{perturbing})^{-3}}$, due to most heating happening while they are in close proximity.
It's inversely proportional to the relative synodic period of the two moons.


texts: Could an astronomical process create elements in the islands of stability?

texts: I was reading about heavy elements recently, and I took note of the theorized islands of stability, and how some the elements involved are considerably heavier than anything we've been able to synthesize so far. Is there any known astronomical process that could create elements well above the 120-proton mark?


texts: Can there be a three-moon system where only two are visible most of the time?

texts:
I am trying to build a moon system for a sci-fi work in collaboration with my boyfriend. He's the main writer and wants there to be three moons circling the planet in a way that most of the time, only two moons are visible and seeing all three or none of the moons is equally rare. I don't have much training in astrophysics (only a university level intro class to it), so my main consideration was that, in the case of Earth's moon, it is only fully/almost non-visible about 10% of its rotation (2-3 days of 28). What else should I consider? If it's possible, how long would each of their orbits be?

For reference, the planet would be orbiting around a Sun-like star and be about 1.13AU away from it (still within the habitable zone, but with a slightly longer year). Each of the three moons rotates on itself as fast as it rotates around Earth, just like Moon does.


texts: What is the typical chemical composition of the most common asteroid types?

texts:
I'm trying to make a semi-scientific accurate game where you can find/mine asteroids. I want the composition of asteroids, and how common they are to be correct. Or at least as close to correct as possible.

Therefore I'm trying to come up with percentages of how common certain types of asteroids are, and what elements are typically present in those asteroids. Of all my research so far I found which elements are found in which asteroids, but never any statistics.

And of course, I understand we don't know much about Asteroids in the first place. Perhaps the data we have is not comprehensive enough to come up with any statistics, in that case, what statistics should I go with?


texts: Birthdate differences calculation relative to earths orbit duration

texts:
I have got a question as I am trying to figure out what the real difference between the birth date of my friend and me is.

I am born on 1983 6th February 7 am. My Friend is born on 1984 7th February 1 am.
1982 was a leap year as the real duration of earths orbit around sun is ca. 365 1/4 days. Okay... But I am struggling to figure out if need to add/subtract 8 hours to my or my friends birthday to figure out what the real difference in our birth dates is, in relation to how long earth orbits around the sun. That leap year is at end of February makes it even harder to me as I don't know how that fits in into the calculation.


texts:
A hopefully simple terminology question:  When you have an object that orbits another object in space, what do you call the object being orbited in relation to the object orbiting?

For instance, you might call the object orbiting the "satellite" of the orbited object, but what would you call the object being orbited?

Orbitee is all i've been able to come up with but it doesn't seem quite right ;)


texts: Why do planets in red dwarf star systems tend to have a higher probability to get tidally locked?

texts:
I have read about about the habitability of red dwarf systems on  Wikipedia, as well as some web articles on similar topics. The problem is, it does not explain why and how it happened. Google search comes up inconclusive. Since then, it became a riddle for me.

We all know that higher mass supergiant stars have stronger gravity than lower mass dwarf stars. Therefore, I can assume that stronger gravity results in stronger tidal forces as well. So, I can conclude:

High mass star systems should have a higher tidal lock probability than lower mass dwarf systems, right?

From that assumption that contradicts the reality, here comes another question:

Does it mean that the tidal lock probability has more to do with the size of the planet relative to the host star size than its mass or gravitational forces?

But here is my other assumption:
Probably a more concentrated (almost point source) of gravity from smaller red dwarf stars locks planets more effectively than a broad giant star.
(It is kind of analogous to a small speaker magnet that has stronger magnetic field compared to the Earth's magnetic field when measured).


texts:
I took many images like the following:

As many of you may recognise, this is a picture of Jupiter and its four Galilean moons. Using these images, I am aiming to calculate the mass of Jupiter by finding the orbital distance and orbital period of each of these moons, and then plugging those values into Kepler's Third Law.

However, this requires a seemingly tedious process of the following sort:

1) Locate the centre of mass of Jupiter

2) Measure the distance to each of the planets

I have a lot of data (many, many pictures). I am hoping that there is a relatively easier (or even more accurate) method of doing all of the above than using software like Gimp to do everything for each image manually. Can anyone recommend anything?


texts: Does the retrograde movement affect the true angular distance between 2 planets?

texts: I need to calculate the relative angular path between two planets in the geocentric view or in other words the number of degrees of a circle one planet travels away from another planet around the Earth. In the heliocentric system I simply subtract the longitude of one planet from the longitude of the other and add n*360 if they made full cycles in between. Would the same work for the geocentric coordinates? Does the loop a retrograding planet makes in the sky actually count as its path? Should I consider the retrograde movement as an optical illusion or include it in the formula and how?


texts:
What are the correct symbols for vernal and autumnal equinox?

I have seen people use both ♈ (\Aries) and $\gamma$ (\gamma) to denote vernal equinox. However, I have never seen the symbol for autumnal equinox. Should it be either ♎ (\Libra) or $\Omega$ (\Omega)?

Are ♈ and ♎ the conventional symbols to use?

Are $\gamma$ and $\Omega$ sometimes used just because they resemble the above symbols?

An alternative name for vernal equinox is First Point of Aries. Is there a similar name (First Point of Libra) for autumnal equinox?


texts: Is it possible to filter radio-waves using another radio telescope?

texts:
When making an observation using a radio telescope, is it possible to filter out noise coming out from a known source by using another telescope that will focus on that noise source?
By filtering, I mean processing the observation on a computer and calculating the filtered image using the second telescope source. Assume that both of the telescopes are connected and can easily sync on time and location and exchange other information.


texts: How would we detect a planet behind the Sun?

texts:
Let's assume hypothetically that Earth has a twin planet on the opposite side of Earth's orbit. Its orbital period would be exactly the same as Earth's and it would always be behind the Sun so directly observing it from Earth would not be possible.

How would we detect the planet's existence short of sending out a spacecraft that could look "behind" the sun and observe it visually? Have we confirmed that there is no such planet?


texts: How much longer is this (July 27th 2018) lunar eclipse than others?

texts:
According to the BBC the lunar eclipse on July 27th/28th 2018 is the "longest this century".

Longest isn't a very good way of describing things, since it's a relative measure without reference to actual numbers, and implies it's somehow longer in some way that might actually matter in a practical way.

How much longer is this lunar eclipse than:

An "average" lunar eclipse?
The next lunar eclipse?
The shortest lunar eclipse this century?
The 2nd longest lunar eclipse this century?

(Feel free to add in any questions/answers I might have missed that may explain "longest" in a better context.)


texts: Milky way: How do we know its appearance?

texts:
How can we know how does the Milky Way look like if we are in it?
Sorry if the answer is evident, I am not an expert.


texts: What happens to the shrinking universe in the presence of the pressure of Hawking radiation?

texts:
Black holes release Hawking radiation. Now assume that the universe after all collapses back again, bringing all matter to a single black hole. I assume that this would bend the whole space-time of the universe as well, wrapping it around the black hole.

Now what happens to the shrinking universe in the presence of the pressure of Hawking radiation?

Could there be a stable point where pressure and gravity are balanced?


texts: Why is this video showing radio waves transmitted from a radio telescope?

texts:
I saw this video at Space.com and I noticed that at 00:05 the animation illustrates waves propagating from space into The Dish at Parks Observatory, but at 00:50 the direction of propagation is reversed! Would there be some reason for transmitting - for example to create an artificial "star" for wavefront correction analogous to adaptive optics at visible wavelengths, or could it be simply a mistake in the animation?

Here are some GIFs from screenshots. You can check the video at the indicated times.

circa 00:05

circa 00:50


texts: Based off of the study that found the universe has a positive curvature, how big would the whole universe be?

texts: This study found that the universe has a positive curvature https://www.nature.com/articles/s41550-019-0906-9. I didn't really want to buy it and see if it says how big the universe might be. I know it didn't have a low enough p-value to be considered confirmed. Is there a big margin of error for the whole size of the universe?


texts:
Where can I get a table with the Moon phase angle for each day ?

It's available  here for a given day, but I would have to input each day of a year to get a full table.

=== NEW EDIT : 2019-09-18 ===

Actually, I'm preparing a calendar of lunar phase with corresponding Moon photo for each day and for a whole year. For this, I downloaded a set of images here from Jay Tanner's website. The name of these images correspond to the phase degree, but when I associate these images with the data from JPL HORIZONS suggested by @Mike G, it doesn't match what I see in the Sky.

How can I associate a set of photo of Moon phases to each day of a given period of time (for instance, the current year) ?


texts: What magnification is required to see detail on Mars / other local bodies?

texts:
I have a 125mm Jones Bird newtonian telescope (very shoddy) with 6x lens (2× + 3×) essentially we were able to see a very small O (yeah that's to scale) with varied shades of red.

Is Mars far away from earth right now relative to the average distance or is it just my telescope not powerful enough?

If I wanted to seriously have a chance at picking up significant features on Mars or perhaps pickup the rings of saturn or the red spot of jupiter, whats the minimum setup that I am going to need?

This setup would run me around 3,000 dollars:

Its named...

Celestron CPC 1100 StarBright XLT GPS Schmidt-Cassegrain 2800mm Telescope with Tripo... https://www.amazon.com/dp/B000ARFND2/ref=cm_sw_r_sms_c_api_x7mSBb39EAS9H

Would this be overkill? For $3,000 is this one of the better choices for local planetary observation?


texts: Why the comets can cross the orbits of planets?

texts:
Why are comets able to cross planetary orbits without colliding with the planets - Why is the comets' orbits elliptical, intersecting all the other planets' orbit.

Why don't they get attracted by the planets when they are in their orbit.

Or, why doesn't the force of gravitation from the planets not attract or compel the comet to rotate around them.


texts: Total apparent magnitude of eclipsing binary system

texts:
This is a question from the 2016 USAAAO national exam, for which no solutions are given:

  An eclipsing binary system has a magnitude $m_p$ = 14.2 during the
  primary transit and $m_s$ = 13.7 during the secondary transit. Find
  the normal (non-eclipsed) apparent magnitude of the system.

I assumed that, as is usual for eclipsing binary systems, the higher magnitude/primary transit refers to the complete eclipse of a smaller, hotter star (say Star B), and the lower magnitude/secondary transit refers to Star B passing in front of a larger, cooler Star A.

To find the normal, non-eclipsed apparent magnitude of the system, usually we achieve a relation like $F_A = kF_B$, where k is a constant. Then, as we know the apparent magnitude corresponding to $F_A$ alone, we could easily calculate that for $F_A + F_B$. However, this is where I ran into trouble. I set up the following equation to attempt to find a relation between $F_A$ and $F_B$: $$m_p - m_s = -2.5log(\frac{F_A}{F_A(1-(R_B/R_A)^2)+F_B})$$

The denominator in the argument of the logarithm, $F_A(1-(R_B/R_A)^2)+F_B$, expresses the flux observed at the secondary transit. But I have no way that I can see to figure out the ratio between radii, and I can't think of any reasonable assumption that would simplify the equation further (such as $R_B << R_A$).

Should this problem be attacked from a different angle? Any help would be much appreciated!


texts: Why do sun spots appear near the equator of the Sun?

texts: I noticed on many examples sun spots are near the equator of the Sun. Why are there no sun spots closer to the poles of the Sun?


texts: Power spectrum of matter in the Universe

texts: I have a picture of a power spectrum of matter in the Universe. What is the connection to Lyman alpha? Please describe it for me (horizontal and vertical and shape).


texts: How bright would the sun appear from the hypothetical Planet Nine proposed by Caltech?

texts: Theoretical Planet Nine, proposed by Caltech's Mike Brown and Konstantin Batygin, is said to have a 15-20 thousand year orbit. Approximately how bright would the sun appear from Planet Nine aphelion and perihelion?


texts: Why can't stars be multicolored like gas giants?

texts: Gas giants like Jupiter and Saturn have bands of different colors in their atmosphere. These are due to the rotation of the planets. Stars rotate too, so why do most stars have patches/blotches of color rather than having latitudinal stripes?


texts: The possibility of rapidly changing the Earths orbit via a passing astronomical object

texts:
I assume that the Earth could be “gently” (without colossal tidal or volcanic catastrophe) displaced by a passing extra solar star, brown dwarf or planet and end up perhaps 10% further away from the Sun?
If so how quickly could this be achieved?
I suppose it would depend on the details, but roughly what combination of distance of approach and mass of object would be best to use for use in a realistic fictional setting? incidentally I assume the orbits of outer planets might well be much more badly affected.


texts: Is the galaxy made of a nebula or the solar system?

texts:
My book says on the topic 'Formation of stars' that a galaxy starts forming by the accumulation of hydrogen gas in the form of very large clouds called nebulae. Then local lumps of gas are formed. These lumps start getting even denser and eventually form gaseous bodies called stars.

That seems a fair explanation but in the topic 'Our solar system' my book says "The nebula from which our Solar system is supposed to have been formed, started its collapse and core formation some time 5-5.6 billion years ago and the planets were formed about 4.6 billion years ago."

So, is the nebula being talked about in the topic 'Formation of stars' same as the nebula being talked about in the topic 'Our solar system'?

This question came to my mind because the nebula being talked about in 'formation of stars' topic might be very large, but when talking about our solar system it is eventually formed into the Sun, so how can they talk about the nebula while describing about our solar system, as the solar system is something within our galaxy.

Any picture helping to visualize will be very nice.


texts: Which planet or moon has all resources that can be used to sustain life in a controlled biosphere?

texts:
Now that we are making it to Mars, continuing onward, in an effort for humanity to civilize other planets, not just setting up residential colonies, but to mine minerals and carry on geological and scientific research, which planet or moon has all resources that can be used to sustain life in a controlled biosphere?

And how can the available resources on that body be converted to suit human requirement?


texts: Would things be exactly the same if the Sun was orbiting the Earth and the Earth was in the center of the Solar System?

texts:
Would things be the same if the Sun was orbiting Earth and the Earth was in the center of the Solar System, or would there be any big difference?

It seems like why people before thought the Earth was the center of the Solar System since it didn't conflict with their experience.


texts:
We have a charged black hole which is negatively charged. For this simple case the black hole is not rotating.
If a negatively charged particle approaches the singularity the electromagnetic repulsion will become stronger than the gravitational attraction causing the object to leave the black hole? But how is that even possible .
There is only one spacetime path available for every object beyond the event horizon and what would this object experience?
Could it travel into the future and into the past after oscillating inside the black hole?


texts:
After reading the paper "The Measured Compositions of Uranus and Neptune from their Formation on the CO Ice Line", I was left with doubts which I would like to clarify.

Firstly, the paper proposes that Uranus and Neptune were created in the CO ice line of the Solar System, which explains several of their unusual characteristics (abundant carbon, depleted nitrogen, etc.).

In the paper, an explanation is proposed for the low D/H ratio of Uranus and Neptune, which is not consistent with that of the comets in their neighborhood, which suggests that the water inside them was not accreted from the protosolar nebula:

  Finally, coupling the D/H observations in Uranus and Neptune with our model where only a small fraction of the water present in the planets interiors is of nebular origin, and the rest originating from the transformation of CO into H2O, leads to a higher D/H ratio for the
  proto-ices that formed the planets. The value found is compatible with internal structure models and the
  formation location of the planets in the same region as
  comets.

Instead, water would be created by reacting the accreted CO with the H2 in its atmospheres. In other words, water would be created within them.

According to the paper, the composition of the CO ice line after 100,000 years was mostly CO, while water represented 1.9% of the total composition. This makes me wonder, why was water scarce in the CO ice line? Is water depletion in the CO ice line related to the high abundance of carbon in that zone?

On the other hand, the authors mention that the large amount of carbon-rich solids allowed the creation of the nuclei of these planets:

  Since CO is the major C-bearing volatile in the PSN [protosolar nebula], its ice line should be very rich in solids, explaining the origin of the high volumetric density of solids needed to form the planets. The high CO abundance in the building blocks implies that planets forming in this region should be very rich in carbon in bulk.

...

  In this paper we showed how the formation on Uranus and Neptune on CO iceline resolves many issues related
  to these planets. The diffusive redistribution of vapor across the icelines increases the local solids density allowing the formation of these planets from carbon rich
  solids but nitrogen poor gas, and lead to planetary interiors consistent with recent D/H measurements.

But what do the authors mean when they say "carbon-rich solids"? Does this mean that the nuclei of Uranus and Neptune are poor in silicates?

All this makes me think that the nuclei of these planets are similar to the carbon planets, which are believed to be made up of carbides, could this be the case of the nuclei of Uranus and Neptune?

However, the authors considered an environment with C/O ~ 1, but carbon planets are expected to form in environments with C/O > 1. Anyway, I can't think of anything other than carbide when the authors mention "carbon-rich solids"...


texts:
Kind of like a shower thought just occurred to me. We've all seen lots of animation about spiral galaxies, how they crash... in virtually all of them, I recall they move in a frisbee way, that is their velocity vector is on the same plane as their disc. That sounds wrong... right? What keeps them from tumbling in a random direction in space? Why can't they move like an American football? Or a tossed coin? You know, all the stars within can still go around merrily, but nothing is keeping the whole spiral from moving in a chaotic way.

Before you say that I'm completely wrong to even speculate that, think of our neighbor Andromeda. Fact: its angle to us is not completely edge-on, perhaps 25deg. Fact: many scientists @NASA & other great institutions made high-confident predictions that we're on a head-on crash course with it. Just those 2 facts mean Andromeda OR Milky Way can't be moving along its own plane (or both, lol).

EDIT: when I said galaxies I meant spirals in particular. Also, I think the question above can be rephrased as: in the case of us & Andromeda, what will we see during the next 4.5Gy? Will we see our sister galaxy tumbling while coming toward us, i.e. its angle changes, its appearance dramatically transforms, not just getting bigger in apparent size?


texts: In practice, can very high magnetic fields significantly alter the dynamics of an astronomical-scale bodies?

texts:
The direct effect of magnetic fields on the dynamics (as in the movements, trajectories etc of the bodies themselves, rather than lower-level phenomena like stellar winds and atmospheric degradation) of astronomical bodies in places like the solar system are so weak that they can be ignored without real consequence. But it seems intuitive that in the vicinity of bodies with extremely high magnetic fields - such as magnetars - that such fields would have a significant or even dominant effect dynamically, requiring electromagnetism to be considered alongside gravity in order to supply an accurate dynamical description of the system.

Considering the fact that the magnetic fields of such bodies range upward of 100 billion Telsa, the fact that the coupling constant for electromagnetism is some 40 orders of magnitude greater than that of gravity, and the fact that magnetic force drops off with the square of distance just as gravity does, it seems odd that such magnetic fields wouldn't have such an effect (at least on other bodies with magnetic fields, as well as bodies with a high content of ferromagnetic materials), but I've never heard any mention of such a thing. So what I'm wondering is if such behavior is expected in the vicinity of highly magnetized astronomical bodies, and if not, what am I overlooking here?


texts: Why does the Simbad page "A.A. Michelson's Jovian Galilean-satellite interferometer" show data for Betelgeuse?

texts:
When searching for things related to How did Michelson measure the diameters of jupiter's moons using optical interferometry? I came across the ui.adsabs.harvard.edu entry A. A. Michelson's Jovian Galilean-Satellite Interferometer at Lick Observatory in 1891 which links to this Simbad page.
But I don't understand what I'm looking at. The title of the Simbad page is

A.A. Michelson's Jovian Galilean-satellite interferometer at Lick Observatory in 1891.

but the date directly below it seems to be Betelgeuse.
I don't use Simbad so I'm not sure exactly how to understand the juxtaposition of the title's
Jovian Galilean-satellite interferometer" with data about Betelgeuse. Is it possible to explain the page's purpose?


texts: What is wrong with this measurement of the synodic period of Mercury?

texts:
I'm measuring the synodic period of Mercury using Stellarium. When measuring the synodic period one needs to choose a reference point to start the measurement, and I choose the point when Mercury is on top of the Sun. This is the start date:

And this is the end date:

Inputting these two dates into a calculator gives a synodic period of 104 days. However, as one can see from Stellarium's data, Mercury's synodic period is actually 115.88 days. This measurement is off by more than 10 days.

Why is there such a large difference? It's not large in the absolute sense, but it seems well above the error margins. For example if instead I shift the start date to 9 April 2021, Mercury is discernibly not between us and the Sun.


texts: Formation of "hot Jupiters" before star ignition

texts:
I'm watching a BBC special on the formation of solar systems, and they're covering the topic of "hot Jupiters" that exist near their host stars. The prevailing theory, according to this 2015 special, is that the planets form farther out, then migrate in. This addresses the issue of their gas being driven off by the host star.

Isn't also possible that these planets formed shortly before the ignition of the host star? The mass that will form the star is already mostly collected, and could hold bodies in orbit, but the heat has yet to begin, and wouldn't drive off gas.


texts:
Wasn't even sure about what the title should be, but I had a thought and I wonder whether it may be possible or not.

Is it possible that there is a star which acts as a mirror and reflects back the light almost as it was received?

My though is that if there is something like that and let's say that the star is far from earth 50 light years, than we could see 100 years back to the past.


texts: Convert apparent magnitude in a filter to a luminosity

texts:
I have data in Johnson B & V filters and I would like to convert the observed magnitudes, m$_x$, into luminosities, L$_x$, over a passband where I already know the distance, d, to the object. x is the band, e.g. U, B, G. I wish to do so using:
$m_x = M_x + 5\log_{10}\Big(\dfrac{d}{10\text{pc}}\Big)$
$M_x = -2.5 \log_{10}\Big(\dfrac{L_X}{L_{\odot}}\Big) + \text{constant}$
Solve for L$_X$. Now if I want to gain a true understanding of the luminosity in e.g. the wavelength range 500-700nm, do I need to correct for the transmission profile of the filter? found here http://svo2.cab.inta-csic.es/theory/fps/index.php?id=Generic/Johnson.V&&mode=browse&gname=Generic&gname2=Johnson#filter
How would be best to do this? Ultimately, I want to work out the fraction of the luminosity found in the B & V band compared to the total luminosity of a black body SED


texts: Transform asteroid rotation to heliocentric ecliptic coordinates

texts:
I'm working with data from the DAMIT database of asteroid shape models.  I'm adding them to a visualization in which the sun is at [0, 0, 0] and the X, Y axes constitute the ecliptic plane of the solar system.

Each asteroid model comes with some attributes that define its orientation and spin:

λ (ecliptic longitude),
β (ecliptic latitude)
P (sidereal rotation period)
φ0 (initial rotation angle)
JD0 (initial date).

I've applied the matrix formulas suggested by the folks at DAMIT:

in which

This is where I get confused.  My understanding is that my visualization uses a heliocentric ecliptic coordinate system.

I set r_ast to the XYZ location of a vertex in my visualization.  I'm not sure this is correct.

Then I compute r_ecl from the equation above.  But I think variables λ and β are angles in a geocentric ecliptic coordinate system and I need to do some transformation into heliocentric ecliptic coordinates.

Is my approach correct and if so, how can I convert the asteroid's rotation to my visualization's heliocentric ecliptic coordinate system?


texts: Computing orbit positions of Jovian Satellites / Moons using JPL data

texts:
I've been trying to build a model of the solar system in a game.  Thus far I've succeeded in placing each of the planets in position using Keplerian elements and formulae from https://ssd.jpl.nasa.gov/?planet_pos  An example for Jupiter is:

               a              e               I                L            long.peri.      long.node.
           AU, AU/Cy     rad, rad/Cy     deg, deg/Cy      deg, deg/Cy      deg, deg/Cy     deg, deg/Cy
-----------------------------------------------------------------------------------------------------------
Jupiter   5.20288700      0.04838624      1.30439695       34.39644051     14.72847983    100.47390909
         -0.00011607     -0.00013253     -0.00183714     3034.74612775      0.21252668      0.20469106

At this point, I want to add several of the Jovian moons, however the same site doesn't seem to provide the same type of data for these moons, perhaps because the moons behave differently.  Unfortunately, my math is not great; I can usually implement something that's written down, but I don't have the wherewithal to work it out myself.

For the Jovian moons, the data is listed at: https://ssd.jpl.nasa.gov/?sat_elem#jupiter  Here is an example for Ganymede:

 Sat.           a       e          w           M        i            node      n             P       Pw      Pnode    R.A.        Dec.     Tilt
 (km)        (deg)     (deg)      (deg)       (deg)    (deg/day)    (days)    (yr)          (yr)    (deg)    (deg)    (deg)
 Ganymede  1070400.    0.0013    192.417    317.540    0.177        63.552    50.3176072    7.155   63.549  132.654   268.168    64.543    0.068

Here they state that the data is "Mean orbital elements referred to the local Laplace planes", as opposed to "Keplerian Elements for Approximate Positions of the Major Planets".

Whilst the first 6 parameters appear to be the same (a, e, w, M, i, node), the Keplerian elements also have "rates", or time derivatives (according to this post: https://space.stackexchange.com/questions/8911/determining-orbital-position-at-a-future-point-in-time).  The forumlae kindly provided by NASA for the Keplerian elements relies on these rates.

If I could understand how to determine the "rates" for the Jovian moons, then I might be able to use the same formula (is this the right thing to do?)  It looks to me like those rates are something I should be able to compute from the other data provided for the moons, however I haven't been able to determine how.

My suspicion is that I either need a different formula for the computation using the Laplace Planes, or I need to compute those 'rate' values and use the same formula I already have.

I'm trying to generate cartesian (x, y, z) coordinates for each Moon where (0,0,0) is the centre of Jupiter itself, for a given date/time (typically "now").

I'm beginning to wonder if I'm barking up the wrong tree on this.  Can anyone shed any light


texts: Black holes are things with immense gravity.Inside black holes gravity is much stronger than any other fundamental forces.But is strong enough to overcome Pauli repulsion?


texts: How does gravity affect the wavelength of light?

texts:
If, hypothetically, me and my rocket powered flashlight were falling straight toward the center of a black hole. The flashlight is a few kilometers behind me in our travels toward the center of the black hole, but since it is rocket powered, it manages to maintain the exact distance to me for a while.

The point is; The distance between me and my flashlight is constant as long as I am observing it.

The photons coming from the flashlight would obviously not be rocket powered - and they would be affected by the black holes gravitation.

Would the light I see from the flashlight be shifted towards red or blue, even though the distance between me and my dear flashlight is maintained?

If so; switching the positions of me and my flashlight, would it change the color I'd observe?

If we turn off the rocket on the flashlight, I assume it would be redshifted regardless of which were closer to the singularity, and the magnitude of redshift would appear to accelerate?


texts: Observing a point 13.82b ly away, 1b years ago

texts:
I understand that we can observe far away galaxies to get an idea how the universe looked like in the past.

Assuming the universe is 13.82b years old, would it be correct to say that if we looked at a galaxy that was 13.82b ly away, we would see whatever happened just after the big bang? If this is correct, what would we have observed had we looked at the same point 1b years ago?

Is this an application for special relativity?


texts: I want a galaxy count database, also how do I use SDSS skyserver to fetch galaxies?

texts:
I'm new to all this and trying to implement galaxy counting. For the initial stage I need raw image data, that is images with galaxies and stars along with a count of how many galaxies there are in the image.

I came across this which seems to have a way to label galaxies

http://skyserver.sdss.org/dr13/en/tools/chart/navi.aspx?ra=179.68929&dec=-0.45438&opt=

but I cannot figure it out at all, I used this page

http://skyserver.sdss.org/dr13/en/tools/chart/chartinfo.aspx

to try to get it to label only galaxies are seen but I got nothing (put G in opt section, did not make a difference).

Does anyone know how to operate the above or where I could get images with lots of galaxies (any number would do) in them along with a count of how many galaxies there are in the image?

I found https://data.galaxyzoo.org/ but traversing it seems impossible


texts:
I am big fan of Asimov's Foundation and I am wondering about the plausibility of some of Foundation's imagined words.

According to this article Terminus was a special world with little metals:

  It was the sole planet orbiting its isolated star and had almost no
  metals. The nearest planet was Anacreon, 8 parsecs (26 light years)
  away. Being on the fringe of the galaxy, there are almost no stars in
  the sky.

Since the planet hosted the first Foundation it is clearly habitable (i.e. atmosphere, no extreme temperatures). However, I am wondering how could it have so little metals if it seems so similar to Earth (habitability-wise) which has lots of metals. Is this possible in our Universe?

I am interested in answers that use current discovered exoplanets information or some articles that deal with planets come to be.

Question: Is it plausible for a planet that is positioned in the habitable area of a solar system to have little extractable metals?


texts: How do I modify redshifts to gain corrected line of sight velocities?

texts:
I'm currently trying to collect the data to run an N-body simulation for 11 of the galaxies in the Local Group where proper motions are known, however I don't understand how to get the required line of sight velocities for the simulation.

I have redshift data from NED for the required galaxies, however by judging what sources tell me, this won't be the required information for the simulation due to our motion around the Milky way's galactic centre.

For example, one source has given the NED redshift as 229 km/s for Carina Dwarf, but the corrected line of sight velocity is 14.3 km/s.

Does anybody know how to convert these redshifts into the desired corrected versions?

Thanks!!